The present invention relates to an apparatus and a method for more accurately determining ground speed of a work vehicle. In particular, the present invention relates to an apparatus and a method wherein at least two different sensors are used to obtain information related to ground speed of a work vehicle, and a control unit determines the ground speed based upon certain of the information from the sensors while the work vehicle is operating in a first ground speed range and based upon certain other information provided by the sensors while the work vehicle is operating in a second ground speed range. A display unit can advantageously be provided for displaying the ground speed determined by the control unit to the vehicle operator. The ground speed thus determined can also be used to more accurately control vehicle functions that depend on the ground speed.
In many work vehicles, such as agricultural vehicles (e.g., tractors), it is desirable to obtain an accurate indication of vehicle ground speed (i.e., the speed of the vehicle with respect to the ground upon which the vehicle travels). The ground speed can be displayed to the vehicle operator, or can be used to control vehicle functions that depend upon ground speed (e.g., by providing control signals for a planting implement coupled to an agricultural tractor). Vehicle ground speed may be measured in several ways. For example, vehicle ground speed may be determined by use of a ground speed radar, if the vehicle is so equipped, which calculates the ground speed by measuring the time elapsed between the emission of radar pulses and the reception of reflections from terrain in front of the vehicle. Alternatively, where the vehicle is not equipped with a ground speed radar, ground speed may be determined by measuring the rotational velocity of a wheel of the work vehicle or a related quantity, such as the rotational velocity of a transmission output shaft. Ground speed may also be estimated by measuring the engine speed, and taking into account the transmission gear ratio and master clutch engagement.
In conventional work vehicles, such as in conventional agricultural tractors, ground speed is measured using a ground speed radar where the tractor is equipped with such a radar. When, however, the tractor is not equipped with a ground speed radar, ground speed is typically measured using a rotational velocity sensor coupled to one of the wheels, or to a transmission gear or transmission shaft.
Each of the above-described devices for measuring vehicle ground speed is limited in certain respects. For example, measuring ground speed using a ground speed radar is more or less accurate depending upon the terrain on which the vehicle is traveling (i.e., depending on whether the radar receives coherent reflections), and also depending upon the ground speed itself. Specifically, in the example of an agricultural tractor operable in both fields (at relatively low working speeds generally below about 8 miles per hour (mph)) or paved roads (at relatively high transport speeds generally above 10 mph), ground speed measurements obtained using a radar are often relatively accurate where the tractor is traveling in a field (e.g., at mid-range velocities of between about 2 and 8 miles per hour). However, the ground speed radar measurements are often relatively inaccurate when the tractor is traveling on roads (e.g., at higher velocities of above 10 miles per hour), especially on wet pavement, and ground speed measurements also tend to be relatively inaccurate at very low velocities (e.g., of below 2 miles per hour).
Measuring vehicle ground speed by sensing wheel velocity or engine speed (or some related quantity) becomes more or less accurate based upon whether the wheels of the vehicle are experiencing slippage with respect to the ground. Slippage may occur due to, for example, travel on wet surfaces (e.g., paved roads) or due to the normal slippage that occurs as a work vehicle such as an agricultural tractor works in a field. Determinations of ground speed based upon measurements of wheel velocity may also become less accurate than estimations of ground speed based upon engine speed at very low velocities (e.g., below 0.5 miles per hour) due to inaccuracies in the sensing of wheel velocity (or the sensing of related quantities).
Since each of the above-described devices for measuring vehicle ground speed is relatively inaccurate under particular conditions, conventional work vehicles equipped with only one type of ground speed measuring device suffer from not being able to accurately measure ground speed under the variety of conditions typically faced during operations of such vehicles. For example, in agricultural tractors equipped with ground speed radars, the measured ground speed tends to be relatively accurate when the tractors are traveling in fields at mid-range velocities, but tends to be relatively inaccurate both when traveling at relatively high transport speeds on paved roads, and also at very low velocities. Meanwhile, in agricultural tractors not equipped with ground speed radars, measured ground speeds tend to be relatively inaccurate under the high slippage conditions (i.e., working a field) which prevail under the conditions within which those tractors were designed to operate.
Accordingly, it would be desirable to develop a system for determining a more accurate indication of vehicle ground speed under a variety of operating conditions than is currently available with conventional work vehicles. Also, it would be desirable to develop a system that is capable of obtaining this more accurate indication of vehicle ground speed through the implementation of one or more conventional sensing devices, including a ground speed radar, a wheel velocity (or transmission output shaft velocity) sensor, and/or an engine speed sensor. Further, it would be desirable to develop such a system that is applicable for use on work vehicles, which are typically operated on a wide variety of terrains over a wide range of ground speeds and under a wide variety of slippage conditions, including under different loads. It would be desirable to provide a more accurate display of ground speed to the vehicle operator, and would also be desirable to more accurately control vehicle functions that depend upon the ground speed.
One embodiment of the present invention relates to an apparatus for determining ground speed of a work vehicle. The apparatus includes a first sensor for producing a first signal representative of a first quantity representative of the ground speed of the work vehicle, a second sensor for producing a second signal representative of a second quantity representative of the ground speed, and a control unit coupled to the sensors. The control unit receives the first and second signals, determines a first indication of the ground speed of the work vehicle if at least one of the first and the second signals indicates that the ground speed is greater than a first level, and determines a second indication of the ground speed if the at least one of the first and the second signals indicates that the ground speed is less than a second level, with the second level being less than or equal to the first level.
Another embodiment of the present invention relates to an apparatus for determining the ground speed of a tractor. The apparatus includes a transmission pickup sensor configured to produce a transmission speed signal, a ground speed radar configured to produce a ground speed radar signal, a control unit coupled to the transmission pickup sensor and the ground speed radar, and a display unit coupled to the control unit. The control unit is configured to receive the transmission speed and ground speed radar signals and to produce a display control signal indicative of the ground speed. The display control signal is based solely upon the transmission speed signal if the control unit determines based upon the transmission speed signal that the ground speed is greater than a first level. The display control signal is based solely upon the ground speed radar signal if the control unit determines based upon the transmission speed signal that the ground speed is less than a second level. The display unit is configured to display an indication of the ground speed of the tractor in response to the display control signal.
Another embodiment of the present invention relates to an apparatus for determining ground speed of a work vehicle. The apparatus includes first sensing means for sensing a first quantity related to the ground speed of the work vehicle and producing a first signal representative thereof, second sensing means for sensing a second quantity related to the ground speed and producing a second signal representative thereof and control means for receiving the first and second signals and for selecting at least one of the first and second signals as being indicative of the ground speed based upon an indication of the ground speed of the work vehicle.
Another embodiment of the present invention relates to a method of determining ground speed of a work vehicle. The method includes sensing a first quantity representative of the ground speed using a first sensor, sensing a second quantity representative of the ground speed using a second sensor, generating a first signal and a second signal in response to the sensing of the first and second quantities, respectively, and providing the first and second signals to a controller. The method also includes determining, at the controller, whether the ground speed of the work vehicle is above or below at least one predetermined level, and obtaining a third signal based upon at least one of the first and second signals, the third signal representing the ground speed of the vehicle. The obtaining of the third signal depends upon whether the ground speed of the work vehicle is determined to be above or below the at least one predetermined level.